The ability to monitor the progression of infectious diseases is limited by the current ex vivo methods of detecting and quantifying infectious agents in tissues. The replication of an infectious agent in a host often involves primary, secondary and tertiary sites of replication. The sites of replication and the course that an infectious agent follows through these sites is determined by the route of inoculation, factors encoded by the host as well as determinants of the infecting agent.
Experience may offer, in some cases, an estimate of probable sites of replication and the progress of an infection. It is more often the case, however, that the sites of infection, and the pace of the disease are either not known or can only roughly be estimated. Moreover, the progression of an infectious disease, even in inbred strains of mice, is often individualized, and serial, ex vivo analyses of many infected animals need to be conducted to determine, on the average, what course a disease will follow in an experimentally infected host.
Accordingly, it would be desirable to have a means of tracking the progression of infection in an animal model. Ideally, the tracking could be done non-invasively, such that a single animal could be evaluated as often as necessary without detrimental effects. Methods and compositions of the present invention provide a non-invasive approach to detect, localize and track a pathogen, as well as other entities, in a living host, such as a mammal.